Porphyrins with exocyclic rings. Part 5. Synthesis of a naphtho[1,2-b]porphyrin.

Abstract

Condensation of 2-acetyl-1-tetralone with diethyl aminomalonate in refluxing acetic acid gave a dihydronaphtho-pyrrole 9a in excellent yield. Transesterification with benzyl alcohol gave the corresponding benzyl ester 9b and subsequent regioselective oxidation with lead tetraacetate afforded the acetoxymethyl derivative 13. Pyrrole 13 condensed with the α-unsubstituted pyrrole 14 to give the asymmetrical dipyrrylmethane 15 and hydrogenolysis over 10% palladium-charcoal yielded the related dicarboxylic acid 16. Acid catalyzed condensation of 16 with dipyrrylmethane dialdehyde 18 gave the dihydronaphthoporphyrin 17 in 44% yield. Alternatively, 17 condensed with two equivalents of pyrrole aldehyde 19 in the presence of HBr to give the a,c-biladiene 20 and cyclization with CuCl 2 in DMF, followed by demetallation with 10% H 2SO 4 in TFA, afforded 17 in 37% yield. Dehydrogenation of 17 with DDQ in refluxing toluene gave 8, the first example of a naphthoporphyrin, in 76% yield. Porphyrin 8 exhibited an unusual electronic spectrum and this may have value in the characterization of sedimentary porphyrins.